Quartz and glass are used not only for the manufacture of optical fibers but also for application as highly reliable materials required for optical communication. However, fabrication of these inorganic materials involves the use of high-temperature processes of low productivity, and therefore a demand exists for finding other easily fabricated and durable organic materials. In this connection, the most reliable material is polyimide which is an organic material that finds wide application in the production of electronic devices.
On the other hand, organopolysiloxanes are another alternative that attracts attention in the field of optoelectronics, due to its excellent characteristics such as high light transmittance, electrical insulation properties, optical stability, thermal stability, etc. Improvements in characteristics of existing polyimide and organopolysiloxane type materials are focused on physical properties of these materials that are most important for transmitting light signals, i.e., non-absorption of light in the communication wavelength range of 1300 to 1660 nm, optical properties without complex refraction caused by orientation of polymer chains, and provision of heat-resistant, water-proof and anti-moisture-absorption properties important for device assemblies.
Japanese Patent Application Publication (hereinafter referred to as “Kokai”) H3-43423 discloses optical elements and optical materials made from a polysiloxane composed of (R1R2SiO2/2) units (where R1 and R2 are groups formed by substituting hydrogen atoms of alkyl or phenyl groups with halogen atoms or deuteriums), from a polysiloxane composed of (R1SiO3/2) (R2SiO3/2) units (where R1 and R2 are groups formed by substituting hydrogen atoms of alkyl groups or phenyl groups with halogen atoms or deuteriums), or from copolymers that contain both units. Furthermore, Kokai H4-157402 discloses optical waveguides produced from similar polysiloxanes. The problems in connection with the aforementioned materials are high material cost associated with substitution of hydrogen atoms of alkyl or phenyl groups by halogen atoms or deuteriums, as well as low resistance to heat because of insufficient curing, and low resistance to solvents.
Kokai 2000-230052 discloses an optical material formed from a polymer composed of (R1SiO3/2 and (R1(HO)SiO2/2 units (where R1 is a fluorinated alkyl group or a fluorinated arylalkyl group). This material is expensive as it contains fluorinated alkyl group or a fluorinated arylalkyl group. Curing of this material requires high temperatures and is time-consuming.
Kokai H9-124793 discloses an optical waveguide produced from a heat-curable polymer composed of (R1SiO3/2) units, (R1(HO)SiO2/2) units, (R1(EO) SiO2/2) units, and (R1R2SiO2/2) units (where R1 and R2 are alkyl groups, phenyl groups, or aforementioned groups in which hydrogen atoms are substituted with halogen atoms or deuterium heavy hydrogen atoms, and E designates epoxy-containing organic groups). The same Kokai also describes an optical waveguide made from an ultraviolet ray-curable polymeric material prepared from the aforementioned polymer and a photopolymerization catalyst. However, since the epoxy-containing organic groups contained in the aforementioned materials are bonded to silicon via oxygen, the material is hydrolysable and therefore is poorly resistant to moisture. Furthermore, the material has low resistance to heat, and its refractive index is prone to changes after heat treatment.
Kokai 2000-180643 discloses the following compositions for use in optical waveguides: a composition prepared from an organic oligomer composed of (PhSiO3/2) units and (R1SiO3/2) units (where R1 is an alkyl group with 1 to 3 carbon atoms, and Ph is a phenyl group or its derivative) and a polymerization initiator; a composition prepared from an organic oligomer composed of (PhSiO3/2) units and (R1R2SiO2/2) units (where R1 and R2 are alkyl groups with 1 to 3 carbon atoms, and Ph is a phenyl group or its derivative) and a polymerization initiator; and a composition prepared from an organic oligomer composed of (Ph(ZCH2O)SiO3/2) units and (PhSiO3/2) units (where Ph is a phenyl group or its derivative, and Z is an epoxy group) and a polymerization initiator. However, the first two of the aforementioned compositions have low photopolymerization capacity, while the third composition is subject to hydrolysis because epoxy-containing organic groups of this oligomer are bonded to silicon atoms by Si—O—C linkages. Furthermore, the above compositions have poor waterproof properties, low resistance to heat, and are subject to changes in their refractive indices after heat treatment.
On the other hand, Kokai S56-38350 discloses an ultraviolet ray-curable coating composition having an epoxy-functional polydiorganosiloxane and a bis-aryliodonium salt, while Kokai H6-41433 discloses an ultraviolet ray-curable coating composition composed of an onium borate and a linear organopolysiloxane having a trimethylsilyl terminal group and an epoxy group. However, since in both compositions the main component comprises a linear diorganopolysiloxane, a cured body obtained from such compositions has low physical strength and resistance to solvents and therefore these compositions are used as solely paper-coating or plastic film-coating for imparting to them the property of peelability or releasability against adhesives.
Kokai H8-193167 discloses a photosensitive resin composition consisting of a polysiloxane of the following formula: (RRSiO2/2), a polysiloxane of the following formula: (RSiO3/2), or a copolymer of the aforementioned polysiloxanes (where R represents an epoxy-containing alkyl substituent or a hydrocarbon group), and an acid-generating agent. However, the above composition finds application only as a resist and is not intended for use as an independent cured body. Specific examples of siloxane copolymers in which carbon atoms of epoxy groups are bonded directly to silicon atoms can not be prepared easily, and there is no explanation relating to such copolymers.